btw: Windows 7 isn't officially out yet. So right now there's only OSX 10.6 a.k.a Snow Kitty
But I've used computers for a long time, and all I can say is: there is very little difference between contemporary OSes. In fact there's more similarity between Win7 and OSX 10.6 than there is between Win95 and Win7 or System7 and OSX. Both are fat kernels trying to masquerade as micro-kernels.
On the real world side, there's the question of driver support and device support which really is only applicable if you intend to use your Mac on certain exotic devices. Otherwise they support a similar range of printers, scanners, video cards, devices, etc. By design and intent, Mac hardware is available from a limited range so the driver support will never matter to most people.
Performance wise: All in all, since both run on the same hardware platform (Intel) and have pretty much the same underlying design, they offer similar performance.
Apps: While it is true that Windows has a much larger range of apps available for it, ask yourself: what are the applications I really intend to use on this machine ? Games ? Productivity software ? If it is FPS games you are after, such as Crysis and Wolfenstein, you'll be better off with Windows. If it is Adobe and other graphic design software you use then of course, this is the traditional strength of the Mac platform. Software such as MS Office etc is available on both platforms.
UI: so it really comes down to what you like as your personal preference. I use both on a daily basis and have no problems switching between them. Just use whatever you are comfortable with. Walk into an Apple store, use the computers there. See for yourself. Walk into a PC store, try out the machines. They might have Win7 RC on display (some did when I was in a Currys last time). Do the tasks you usually do and see how comfortable you are doing them.
Finally: don't ever get swayed by ads from either MS or Apple. Remember one thing: you're the consumer, at the end of the day they're just companies not charities or your best friend. They just want your money. It's
your money so spend it wisely.
And of course, be happy with whatever you chose !